If you don't have a GST/HST number, then you can leave that space empty on your self-employment forms.
If you are not sure if you need to register for a GST/HST account, you will need to contact the Canada Revenue Agency (CRA) and confirm it with them.
If you are in Canada or the United States, you can call the CRA at 1-800-959-8281. If you are elsewhere, you can call 613-940-8495. This page has more ways to contact the CRA: Contact the Canada Revenue Agency
